libvirt users - Mar 2017 - Get PID of a domain's QEMU instance from its domain ID

Hello,

I cannot find a way to retrieve PIDs of QEMU instances from libvirt domains'
IDs (I'm using libvirt C API). I recognize it sounds like a bad idea doing
so
(and I know PIDs are explicitly made not available, as I gathered from the
source code and on your IRC channel) but I need that to use the perf_event_open
syscall in order to gather statistics on my QEMU/KVM guests. I also know
libvirt now supports some perf events but only a few and I need more. I could
submit patches to add them and I will definitely consider that but in the
meantime...

What would be the best way to get those PIDs? I tried using the XML file but
PID is hidden in there too. I took a look at QEMU Machine Protocol. Now I'm
going to walk /proc and match on guests names but it is not that elegant.
Any ideas?

Thanks,

Thibaut S.

On Mon, Mar 20, 2017 at 02:11:21PM +0100, Thibaut SAUTEREAU
wrote:
>Hello,
>
>I cannot find a way to retrieve PIDs of QEMU instances from libvirt
domains'
>IDs (I'm using libvirt C API). I recognize it sounds like a bad idea
doing so
>(and I know PIDs are explicitly made not available, as I gathered from the
>source code and on your IRC channel) but I need that to use the
perf_event_open
>syscall in order to gather statistics on my QEMU/KVM guests. I also know
>libvirt now supports some perf events but only a few and I need more. I
could
>submit patches to add them and I will definitely consider that but in the
>meantime...
>
>What would be the best way to get those PIDs? I tried using the XML file but
>PID is hidden in there too. I took a look at QEMU Machine Protocol. Now
I'm
>going to walk /proc and match on guests names but it is not that elegant.
>Any ideas?
>
`ps aux | grep $UUID | grep -v grep` ??
>Thanks,
>
>Thibaut S.
>
>_______________________________________________
>libvirt-users mailing list
>libvirt-users@redhat.com
>https://www.redhat.com/mailman/listinfo/libvirt-users

On Tue, Mar 21, 2017 at 12:06:25 +0100, Martin Kletzander
wrote:
> On Mon, Mar 20, 2017 at 02:11:21PM +0100, Thibaut SAUTEREAU wrote:
> > Hello,
> > 
> > I cannot find a way to retrieve PIDs of QEMU instances from libvirt
domains'
> > IDs (I'm using libvirt C API). I recognize it sounds like a bad
idea doing so
> > (and I know PIDs are explicitly made not available, as I gathered from
the
> > source code and on your IRC channel) but I need that to use the
perf_event_open
> > syscall in order to gather statistics on my QEMU/KVM guests. I also
know
> > libvirt now supports some perf events but only a few and I need more.
I could
> > submit patches to add them and I will definitely consider that but in
the
> > meantime...
Looks like you are looking for:
http://libvirt.org/formatdomain.html#elementsPerf

and 

http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainGetPerfEvents
> > 
> > What would be the best way to get those PIDs? I tried using the XML
file but
> > PID is hidden in there too. I took a look at QEMU Machine Protocol.
Now I'm
> > going to walk /proc and match on guests names but it is not that
elegant.
> > Any ideas?
Just to re-iterate. We hide it because users should not fiddle with the
VMs behind our backs.
> > 
> 
> `ps aux | grep $UUID | grep -v grep` ??
This will obviously work, but we won't give you an elegant way since we
don't want you to know the pid.